Guar gum is obtained from the endosperm of the guar (also known as clusterbean) plant Cyamopsis tetragonoloba (L.) Taub. Guar gum powder is typically produced by mechanically separating the endosperm (also known as guar “splits”) from guar seed and hydrating the endosperm material in basic solution, followed by mechanical milling and drying to form the guar powder. U.S. Pat. No. 5,536,825 to Yeh et al. discloses techniques that may be used to form guar gum powder from guar splits.
Guar gum powder itself is comprised mostly of a water soluble, non-ionic polysaccharide consisting of a linear backbone chain of mannose linked together by β-(1-4) glycosidic linkage, and which forms branch points from the 6 position to galactose units through α-(1-6) linkage. Processing techniques have been disclosed to improve or modify guar gum powder for food grade applications, drilling and hydraulic fracturing fluids, and other industrial applications. U.S. Pat. No. 4,754,027 to Applegren describes a technique for processing guar gum powder to produce an ingestible guar end product.
Many ophthalmic formulations comprise compounds that provide lubricity and other desirable properties. When these formulations are instilled in the eye, the properties of such compounds can prevent undesirable problems such as bioadhesion and the formation of friction-induced tissue damage, as well as encourage the natural healing and restoration of previously damaged tissues. Guar and guar derivatives such as hydroxypropyl guar (HP-guar) are used to provide characteristics such as lubricity to ophthalmic formulations.
Guar gum powder can be processed and purified by dissolving the powder in aqueous solution and adding organic solvents to induce precipitation. However, the precipitate thus formed often flocculates, forming a gum or viscous semi-solid having a fibrous character. Such precipitates tend to foul filtration and mixing equipment, making it difficult or impossible to utilize the guar material in a commercial-scale process for manufacturing aqueous pharmaceutical products, e.g., sterile ophthalmic solutions.
Prior approaches for addressing this problem have required that the resulting precipitate be mechanically milled or cut, either before or after a drying step, to render a dry solid. For example, EP 0514890 to Maruyama et al., discloses a method for purifying polysaccharides, including guar gum. The method of Maruyama requires the use of a precipitate cutter to generate the desired polysaccharide particle sizes for further processing and preferably uses isopropanol solution to induce precipitation. However, the dry solid thus rendered is of very low density, making it more expensive and inconvenient to ship and store in bulk quantities. In addition, this process has long processing and drying times due to the large amount of organics remaining after precipitation.
Previous disclosures have discussed the usefulness of guar and borate combinations for use in topical ophthalmic formulations, particularly gelling formulations. U.S. Pat. No. 6,403,609 to Asgharian describes such guar/borate combinations, but does not disclose a process for producing guar from guar gum powder.